PCT patent application Serial No. PCT/US2014/12738, filed Jan. 23, 2014; and U.S. Provisional Application No. 61/757,005, filed Jan. 25, 2013, are incorporated herein by reference in their entirety.
It is well known in the HVAC (Heating, Ventilating, and Air Conditioning) industry that manufacturing improvements in Mechanical Contractor duct shops have been highly automated through the use of automatic plasma cutting tables for making fittings, automatic coil processing lines for making rectangular duct, automatic seamer machines for closing duct seams and automatic duct flange corner plate inserter machines for inserting and crimping duct section flange corner plates securely in duct section end flanges. Round and oval duct sections are automated with machinery as well.
Prior Art documents evidencing representative known inserted corner plates and related flanges and other apparatus, are shown in Heilman et al. U.S. Pat. No. 4,466,641 and Fischer et al. U.S. Pat. No. 4,579,375. Representative known integral duct section flanges and inserted corner plates are shown in Goodhue U.S. Pat. No. 5,321,880. Fischer et al. U.S. Pat. Nos. 6,460,573 and 6,810,570 teach fasteners through corner plates and through integral duct flanges and respectively threading screws through corner plates and flanges. Fischer U.S. Pat. No. 8,172,280 discloses further improvements to inserted corner plates by providing pre-formed holes for threadedly receiving fasteners, which reduce required threading force.
It is also well known in the industry that improvements are needed for field installation of duct sections on the job sites. Many Mechanical Contractors are preassembling duct sections in shops and shipping them to the job site in multiple section assemblies wherever possible in order to control costs by reducing labor and improving quality. As an illustrative example, for some commercial installations, such as sports arenas, halls, auditoriums, large factories, malls, etc., it can be advantageous to pre-assemble several duct sections on the floor or ground, then lift or hoist them as an assembly, e.g., 25 or more feet in length, to a ceiling area that can be quite high, for example, 30 to 40 feet above the floor, or higher. The workers will then assemble them to an existing duct system already in place. Moving such large assemblies at such elevations can be imprecise, and is often accomplished by workers at an opposite end of the assembly pushing and/or pulling that end, to achieve precise placement and alignment of the end to be assembled with existing ducts.
Presently, aligning flanged duct sections is typically done by inserting drift pins through holes in the inserted corner plates when the duct is lifted or placed into close proximity with duct sections already positioned or hanging in place. A sticky adhesive gasket is typically adhered to one duct section and if the gasket is adhered to the other section while the sections are improperly or mis-aligned, the gasket is often difficult to detach and can be ruined, requiring removal and application of a new gasket, which is costly and time consuming. Disturbing the gasket causes openings and creates leakage problems. If this happens, more time and costs are incurred to repair the leaks adding to time required and worker frustration. A problem encountered when attempting to avoid premature adhesion is that the drift pins, while useful for general aligning, because of their tapered shape and the presence of the gasket between the duct sections, typically do not facilitate final close alignment of the duct sections for final assembly, and provide little or no ability to hold the duct sections apart while not yet fully aligned to allow workers to manually align the duct sections, such that unintentional gasket contact and adhesion can occur. Application of adhesive tape gasket is cumbersome as the tape is more readily applied with the duct section placed on the floor or ground in a vertical position with one flanged end down and the end to which the tape gasket is to be applied up. The top end is then taped with the gasket round about the duct section flange using gravity to help hold the tape in place on the flange. For a conventional duct section five feet long, this requires the taping process to be done at eye level for most workers. The tape gasket must be bent sharply around the inserted corner plate area of the flanged end of the duct section.
As noted above, for some applications at some point in the assembly process there are often several assembled duct sections on the floor or ground, that must be lifted to assemble to a duct system in a ceiling area that can be 30-40 feet or higher above the floor or ground (e.g., in a sports arena or auditorium, factory, etc.). To apply the tape with the duct section horizontal risks the tape falling off the flange if adequate adhesion isn't achieved, e.g., due to an unclean surface or during cold conditions where the adhesion is poor, etc. This problem is worsened at the tightly bent portions of tape placed around the inserted corner plate area. The tape gasket has a certain amount of memory for successful gasket performance requirements which adds to the possibility of movement and loosening especially at the bent areas of the gasket.
Once the duct sections are positioned in end to end relationship, finally aligned and brought together, as additional steps, clamps are typically applied to the flanges to hold them together in the aligned condition, and the drift pins are removed. Once the clamps are in place and the drift pins are removed, the drift pins are replaced by bolts (typically carriage bolts) through the corner plates, washers are placed over the bolts, and nuts threadedly engaged with the bolts to fasten the duct sections together through the corner plates. Only one fastener is typically used through one hole through each inserted corner plate and passes through only the corner plates. After the corner plate bolts are tightened, typically clips are securely installed using a tool to manipulate them over the outer edges of the duct section flanges in spaced relation to hold the duct section flanges forcibly against each other to provide a sealed connection. Two inch pressure class and lower SMACNA rated duct sections are sometimes fastened together with Tek screws drilled through the mating flanges. Higher pressure class duct sections are limited to spaced apart clip connections along mating duct section flanges. Observed shortcomings of this manner of final duct assembly include that the component parts are costly and must be maintained in inventory, it requires substantial labor, and is time consuming. There is also an attendant possibility of danger when assembly is done at ceiling level, of dropping component parts, so as to injure persons or equipment below. In this latter regard, conventional known clips used to clamp the flanges are known to slide down and fall from the ducts.
Fastening the assembled duct sections using Tek screws or other sheet metal screws has the desirable advantage of eliminating clips. However, presently when using Tek screws, it is still required to have the mating flanges clamped or otherwise forceably held together. This is because if a threaded fastener is threadedly engaged with two spaced apart flanges simultaneously and rotated, the fastener will pass through the two flanges at the same rate and will not bring them together. To bring the flanges together, if the fastener is not threaded all of the way to the head, the flange closer to the head of the screw will have to reach a space between the endmost thread and the head of the fastener, or, if the fastener is threaded all of the way to the head, the threads of the fastener or the flange closer to the head will have to be sufficiently obliterated, such that threaded progression through that flange will halt during the rotation and the other flange will continue its threaded progression toward the closer flange to bring them together. Shortcomings of fastening in this manner include that it is imprecise, and if the space between the head of the fastener and the endmost thread is too small to accommodate the closer flange, part of the threads will still have to be obliterated, and if the space is greater than the thickness of the two flanges and any gasket or sealant between them, the fastener may not bring the flanges close enough together to achieve the required seal. As another possible shortcoming, use of battery operated tools is currently popular for assembling ducts, and if the fastener is threadedly engaged with the flanges using a battery operated driver, the energy consumed to provide the torque required to rotate the fastener while threadedly engaged with the two flanges, and to obliterate the metal threads, will shorten battery life, requiring additional batteries, more frequent charging and related inconvenience and expense.
Addressing hanging ducts, in one representative manner of hanging, trapeze style hanger supports are positioned below the duct sections with standard overhead threaded rods placed through the trapeze style hanger supports for larger duct sections by putting nuts and washers above and below the threaded hanger support and tightening them in place. When installing, the duct must be lifted, e.g., about an inch or so, above its final position so that the trapeze support hangers can be fastened in place, and the duct is lowered onto the support. For smaller lighter ducts, slide lock clamps and cables are used by wrapping the cables around the duct and overhead supports such as beams or structures. Flat metal strips are also used to support and hang duct sections. As an observed shortcoming of use of hanger cables wrapped directly about the ducts, it has been found that normal operational vibration of the duct can cause the cable to “saw” or “cut” into the duct walls resulting in the problem of leakage. As a manner of reducing complexity of hanging, it would be desirable to incorporate hangers into the duct assembly, and more particularly to attach hangers to the flanges of the duct sections as they are assembled so that the hangers will be located over and directly support the assembled duct joints. However, with the current manner of duct assembly involving steps of aligning and bringing together with drift pins, clamping, removing the drift pins, then inserting bolts through the holes, it would be difficult to incorporate addition of hangers, as inserting them between clamped flanges would be difficult, and they would have to be blindly aligned with the holes through which the bolts are inserted. If it is attempted to place the hangers on the drift pins prior to assembly, there is nothing to hold the hangers on the smooth tapered length of the drift pins, and the weight of the hangers can cause the drift pins to tilt down and increase the difficulty of properly aligning the duct sections. There is the possibility of placement of the hangers on the ends of the bolts after passage through the crimped flanges and the inserted corner plates, but then the hangers may interfere with crimped edges of the associated flanges, and/or require an additional nut for securing. The crimp may also be poorly done and loosen under load.
As another issue for consideration, smaller duct sections are often used at locations in duct systems farther from the larger supply duct sections and are typically connected to the larger duct sections by transitioning from flanged ducts to slip- and drive-on connections. Flanged ducts are flanged top and bottom and on both sides. The flanges may be integrally formed or slide on style. As many duct sections as are practical to lift into position safely are often pre-connected at floor level to provide better access to and control of the connection process and efficiency. Difficult to reach flange connections are more accessible with the use of magnetic socket wrenches and extensions that are power driven rotationally. Job site conditions such as stored materials for other contractors often make it desirable to get the duct sections in place as quickly as possible for safety and efficiency, and to avoid and reduce delays and interruptions of other job site work. In this regard, scheduling duct section lifting and hanging is often also difficult due to other job site work, e.g., presence of contractors such as plumbers, electricians and others needing the same work space.
Thus, what is sought is a manner of assembling and hanging duct sections using inserted corner plates, that is more efficient and productive, particularly in terms of field or job-site assembly, simpler, and easier than known methods and systems, and overcomes one or more of the shortcomings and limitations set forth above.